Undercover Pursuit by Susan May Warren

Luke Dekker is a member of Stryker's team and is on assignment.  He is to protect a bride on Isla Mujeres, an island off of Cancun - a bride marrying into a drug cartel family.  A bride willing to set the stage for the capture of the groom's powerful uncle.
Scarlett Hanson is a last minute addition to another wedding on the island, her sister's.  She was going to be her sister's maid of honor until her jealous sister took her out of the wedding.  But now the new maid of honor has had an accident and can't make it.  Scarlett is suddenly back in the wedding and rushing to the island.
When Scarlett and Luke end up in the same cab, Luke mistakes Scarlett for the woman Stryker arranged to be his "fiance" as Luke carries out his assignment.  When Luke finally realizes the trained operative has been delayed and this woman he has already introduced to the "family" is really a temp from Minnesota...
Warren has written another great romance/intrigue novel in the Missions of Mercy series.  There is great humor as the two weddings unfold - as people and plans get really messed up.  There is serious intrigue when the groom's father suspects Luke is not who he says he is.  And there is romance as Luke and Scarlett struggle with the feelings they have for each other.

Love Inspired Books, an imprint of Harlequin, 218 pages.